Blown up power supply question.

stardust steve (Steve) · #1 07-05-2013, 07:12 AM

Hi. I have a powertech 13.8V 12 A power supply that i use to power my mount and last night when packing up there were some bare wires and the + and - touched

. It gave a pop sound and then the red light faded in and out before turning off and not turning back on.
I'm thinking that it's headed for the rubbish bin but thought i would ask here first if it can be repaired or a throw away. It cost about $70 from Jaycar and is similar to the one in the pic.
I checked the fuse and the fuse is ok which i though was strange, makes me think something is fried on the inside.
Cheers,
Steve.

ZeroID (Brent) · #2 07-05-2013, 08:48 AM

Worth opening up to take a look inside. Look for burnt smelly components. Possibly taken out the regulator chip but maybe just a capacitor or other minor component.

multiweb (Marc) · #3 07-05-2013, 09:00 AM

I think I had 4 of these. They all eventually blew and I only occasionaly used them. It's not like I image 24/7.... They're not very reliable. I'd stay away from them.
I use these now. Still going.

DavidTrap (David) · #4 07-05-2013, 10:29 AM

They now advertise these as "workshop supply for testing". Have seen many posts talking about their lack of suitability for our needs. I have one that has been working fine for years, but I don't hold my breath for it's long term survival.

DT

johnt (John) · #5 07-05-2013, 11:44 AM

Quote:

Originally Posted by stardust steve

Hi. I have a powertech 13.8V 12 A power supply that i use to power my mount and last night when packing up there were some bare wires and the + and - touched

. It gave a pop sound and then the red light faded in and out before turning off and not turning back on.
I'm thinking that it's headed for the rubbish bin but thought i would ask here first if it can be repaired or a throw away. It cost about $70 from Jaycar and is similar to the one in the pic.
I checked the fuse and the fuse is ok which i though was strange, makes me think something is fried on the inside.
Cheers,
Steve.

Hi Steve,

I am guessing that the fuse was on the 240V side? If the fuse is on the 240V side, that would explain it not blowing in this case. It is always a good idea to also have a fuse on the 13.8V side to stop the shorting out from damaging the power supply (in your case say a 12A slow blow, or even lower if you are never going to come close to drawing 12A). Ready made wired fuse holders that can be simply connected to the + 13.8V output are available from Aztronix, and probably Jaycar. Also, some better power supplies have short circuit protection at the 13.8V output, but obviously not in this one.

Do you know if it is a "switch mode" like the one in the photo? The best way to tell is the weight. If it's quite light (no transformer), it probably a "switch mode". Otherwise if its heavy, it is probably a Transformer type.

For my use, I have tended to stay away from the switch mode supplies and I prefer the Transformer types. They tend to be cleaner (less noise in the 13.8V output), have a simpler circuit that can be easier to repair, and tend to take more abuse, (ie. the occasional accidental short circuits, especially with the output protection circuitry).

Jaycar does still sell some "Transformer" power supplies. They are those white "Powertech" supplies at the 5A, 10A, 20A and 30A levels, and I'm pretty sure they have short circuit protection. I have a 20A and a 30A version, and I can tell you that I have short circuited the 20A many times without a fuse, and it's still fine. But, as I said, a fuse at the output takes care of the shorts anyway, if you don't mind replacing fuses.

Anyway, if you would like me to take a quick look, I would be willing to. I will either quickly find something simple and fix it (or tell you what to fix), or just say its not worth it. Again, if its a Switch mode" type, it will probably not be an easy fix.

Send me a PM..

John

h0ughy (David) · #6 07-05-2013, 02:16 PM

those at astrofest know that i have been through a fair amount of these - 5 to be exact and one 20A power supply. pop fizzle and smoke. they dont like brownouts, not at all. I use a ups in the system before a very heavy duty power supply now - no more switchmodes

Osirisra (Ken) · #7 07-05-2013, 03:00 PM

Hmm I have one of these that I have always been a little dubious about. I run it powered from a Honda generator and then a fused 12v RIGrunner board to the equipment.

Any good supplies to recommend with out breaking the bank?

wasyoungonce (Brendan) · #8 07-05-2013, 03:40 PM

They are little cheap switch-mode PSUs of reasonably poor design. I have one of these Powertech switch modes and I use it just for dew heater control and heat...nothing else. It it blows...I'll just toss it.

A far better and better and cheaper option is to use a computer ATX power supply as a +12VDC supply. They offer far better protection & control of voltage rails...in this case +12V, are reliable and need little in the way of parts to modify and use. However I have noticed most computer PSU's you sometimes need to modify the +12V DC out with a low pass LR or LC filter to stabilise inrush current spikes on switch on.

FWIW

wasyoungonce (Brendan) · #9 11-06-2016, 04:35 PM

Digging up old thread.

I just destroyed my Powertech 13.8V PSU, 20A version, I really only use it for dew heater power. The damage was caused by me reversing polarity and trying to power a friends car amplifier I was to fix.

Anyway this is a powerteck is a cheap typical SMPS that comes in may versions of output rating. I've found the damaged parts,Q1/Q2 switching transistors and some bad caps and are waiting for these but wanted to put it out there that these units can be repaired they are simple. On another note...I am dismayed that this unit appears to have no over voltage nor any other protection built in.

So apart from repairing it I'll be looking at adding some much needed protection like: Overvoltage shutdown; maybe current limit shutdown; basic things but sadly needed. I'm also reverse engineering it into a PCB CAD drawing for the future.

Anyway FWIW, these can be repaired easily but they really are cheap and rough.

A typical computer PSU has much better protection than this unit. In fact I have modified a computer PSU to run @16V DC out for my Gemini 1 mount power, as well and modifying the protection ccts.

Anyway...FWIW and maybe someone in the future will face this same issues and my upcoming drawings and musing might help!

More to follow.

Brendan

wasyoungonce (Brendan) · #10 15-06-2016, 05:17 PM

Ok here is a qick and dirty schematic and PCB drawing of my powertech 20A 13.8V unit. I'm still waiting for Q1 & Q2 to arrive from UTS to fix my unit.

I've replaced caps, some diodes but not really a lot. It's an easy system to repair and as noted there is little to none in the way of voltage and current foldback.

The drawings are really quick and dirty forgive me but I've included a zipped file of the PCB/Schematic for eagle PCB cad. I've done some poetic justice to some parts used....in lieu of drawing my own switchmode transformers.

Hopefully my transistors will arrive soon.

Brendan

wasyoungonce (Brendan) · #11 23-06-2016, 01:20 PM

Ok parts arrived...unit fixed. The fail was a dead switching transistor Q2 (D209L). Although the output voltage is a little low....12.2V Vs 13.8. I'd have to fiddle with the reference calibration resistors on pin 1 of TL494 (IC1). Since its only for dew heating...I'll leave it for now.

trent_julie · #12 23-06-2016, 10:32 PM

We all know that sensitive electronics do well to protect the fuse

wasyoungonce (Brendan) · #13 24-06-2016, 01:28 PM

Quote:

Originally Posted by trent_julie

We all know that sensitive electronics do well to protect the fuse

Ain't that the truth!

Also forgot to mention, the replacement parts came from UTsource (they were not freely available). A parts provider I've got good parts from before. This time...the Transistors looked decidedly 2nd hand, lots of solder over the legs, yet the legs were full length not cut down.

I could go on but suffice to say they looked a bit dodgy but they do appear have worked ok.!

I checked them prior to install (with multimeter) their Vf junction voltages were spot on and my Mega328 transistor tester (Karl-Heinz Kübbeler knock off) showed them to be same fwd junction voltage ok and Beta gain of 15...but for some quirky reason my tester doesn't show any other transistor parameters apart from junction ident. Think I need a new one.

I also got FR157 diodes from them. They looked even more dodgy. They were quite a bit smaller and their ident part print on the body was very very poor quality. I didn't use them the original were ok.

So over all ...decidedly unimpressed this time.